There are hundreds of photo apps in the App Store and sometimes, it can be quite an effort to sift through them all to get the ones you think will be most useful. I wrote previously about five fantastic paid iPhone photo apps and it’s about time I mentioned some free photo apps with rather impressive features.

Impression – this app adds a watermark to your image which can have several uses. iPhone photos may be easily copied without your consent once you upload them in the internet. A watermark acts as a deterrent and makes people think twice before grabbing the photo. The watermark of this app can also be anything, from your name, to a short phrase, to a photo title, as long as it is no more than 60 characters. You also have the option to add the copyright symbol or not. The text size can be adjusted by pinching or stretching the text and you may also adjust its opacity and placement in the image. Just be aware that it will save to the original shot so use a copy image if you want the original to be left untouched.

PS Mobile – if you want an efficient and user friendly photo editing app, then this app from the makers of Adobe Photoshop could be what you’re looking for. It doesn’t have that many features but then it’s free so I can’t complain at all. Most of the tools are basic for quick editing such as crop, rotate, flip, and exposure, saturation and tint adjustment settings. It also has several filters and effects such as Vibrant and Soft Black and White. Once you’re done editing, you may upload it to photoshop.com, its website where you can set up an account and get a free 2 GB worth of photo storage. This app is so easy to understand that even if you have never used it or Photoshop before, you’ll quickly get the hang of it.

iRetouch Lite – this is one photo editing app that’s quite a powerhouse even though it is free. It has several editing tools such as smudge and clone stamp, and you can adjust the image brightness, color and hue, among many things. From selective desaturation to blemish removal, this app is great for spot editing. The buttons do need some getting used to and your hand needs to be steady since the slightest flick of your finger while editing can affect the image.

Polarize – if you miss the days of the Polaroid camera, you can download the Polarize app and create images that look as if you were using the real deal. This app takes the image in a square format and adds a border where you can write atag or caption (14 characters max) below the image. Most of the images from this app end up with a soft blue green color cast just like how images from Polaroids would look. The effect can appear vintage and make one become quite nostalgic.

GorillaCam – from Joby, the creators of the Gorillapod, that flexible tripod, comes an app packed with features that can seldom be found in other photo apps. Among its many features is a self-timer, a time-lapse function, a ‘press anywhere’ capability which means your whole screen becomes one giant shutter release button, and an unlimited rapid-fire so you can now take pictures at high speed just by keeping the shutter button pressed. If your iPhone is 3G or 3GS, you will find the separate accessory, Gorillamobile, handy as it is a flexible tripod specifically designed for the iPhone.